The current development of mobile communications changes with each passing day and has rapidly entered a 4G era from a 3G era, and the popularity rate of mobile phones is very high and is increasing year by year. Moreover, with the increasing complexity of geographical and electromagnetic application environments, the requirements on the cost of a base station antenna and on such performance indexes as high gain, low sidelobe and the like are also steadily increasing. Base station antennas are typically implemented as phased array antennas that have a plurality of individual radiating elements that are disposed in one or more columns.
In order to change the coverage of the base station antenna, a mobile operator usually changes the elevation or “tilt” angle of the base station antenna. Currently, a mainstream base station antenna is mostly an electrically tunable antenna with an electrically adjustable tilt angle. The introduction of antennas having electrically adjustable tilt angles provides convenience for an operator, since the tilt angle of the antenna can be adjusted without the need for a technician to climb an antenna tower and mechanically adjust the tilt angle. As a result, the safety of the operator can be guaranteed, the workload is reduced, and the work efficiency is improved.
The tilt angle of a base station antenna is typically (but not always) set to an angle of less than 0 degrees with respect to the horizon, and hence the tilt angle of a base station antenna is often referred to as the “downtilt” angle. The downtilt angle of the antenna is set to not only reduce the neighborhood interference of a cellular network and effectively control the coverage of a base station and the soft switch proportion of the network, but also is set to enhance the signal intensity within the coverage of the base station, so as to improve the communication quality of the entire network.
A phase shifter can achieve beamforming of an array antenna, can enable the downtilt angle of the antenna to be continuously adjustable, is an important part of the electrically tunable antenna of the base station, and plays a critical role in adjusting the tilt angle, suppressing sidelobe and obtaining a high gain and the like.
FIG. 1. shows a vertical plane directional diagram of a conventional base station antenna with a 0-degree tilt angle. The sidelobe suppression performance of the antenna is focused on herein.
FIG. 2 is a schematic diagram illustrating a phased array base station antenna having five radiating elements. FIG. 2 further illustrates changing the phases of the individual radiating elements in an array antenna to electrically adjust the tilt angle of the antenna. As known by those of ordinary skill in the art, conventional base station antennas typically include one or more of the arrays of radiating elements such as the array shown in FIG. 2. In order to achieve a variable electric tilt angle, the phases of the radio frequency (“RF”) signals transmitted or received through the antenna units (also referred to interchangeably herein as “radiating elements”) in the array antenna need to be changed, thus allowing the phases of the RF signals at the radiating elements to have a relationship similar to an arithmetic progression. Additionally, in order to obtain better sidelobe suppression, there are also certain requirements on the amplitudes of the RF signals fed through each radiating element. The binomial amplitude distribution of an array antenna having five radiating elements that is shown in FIG. 3 is a common amplitude distribution form that may be used to provide sidelobe suppression. Of course, many other kinds of amplitude distribution forms are also known.
As mentioned above, the phase change and the function of providing a certain form of amplitude distribution are usually achieved by a phase shifter network. Conventional phase shifter networks are generally divided into two types: a. distributed phase shifter networks (as shown in FIG. 4); and b. lumped phase shifter networks (as shown in FIG. 5).
a. Distributed Phase Shifter Network
As shown in FIG. 4, the so-called distributed phase shifter network individually controls the phases of each of the radiating elements in the array antenna by a phase shifter system.
The advantages of this structure lies in that each antenna oscillator (which term is used interchangeably herein with the terms “antenna unit” and “radiating element”) in the array has independent phase control, so a nearly perfect vertical plane directional diagram can be obtained, and very good sidelobe suppression can be achieved at each downtilt angle.
The disadvantages of this structure are it requires a greater number of individual phase shifters (namely one for each radiating element) resulting in a large size and an increased cost for the phase shifter system.
b. Lumped Phase Shifter Network
As shown in FIG. 5, in the so-called lumped phase shifter network the phases of a plurality of sub-arrays of radiating elements in the array antenna are controlled by the phase shifter system, and the radiating elements in each sub-array are connected by a power divider. However, the phase differences (if any) between the radiating elements in each sub-array are constant and invariable.
The advantages of this structure lie in that the phase shifter system is small in size and low in cost.
The disadvantages of this structure lie in that as the phases of all of the radiating elements in the array cannot be independently controlled, and hence the sidelobe suppression may be worse.
In addition, the existing multi-port phase shifter generally adopts a serial form, and a level of phase shift error will be superimposed once a level of phase shifter is additionally connected in series, such that when the phase shifter is connected to the array antenna, the phase error of output ports of the phase shifters on both ends may be larger, and the phase error of each radiating element in the array antenna may be inconsistent.